1. Field of the Invention
The present invention relates to a wheel braking control apparatus for use in vehicles, such as automobiles. More particularly, this invention relates to a wheel braking control apparatus having an antiskid (antilock brake) function.
2. Description of the Related Art
A wheel braking control apparatus having an antilock brake function or antilock brake system (hereinafter referred to as ABS) to prevent locking of wheels at the time braking is disclosed in Laid-Open Japanese Patent Publication No. 64-74153.
The antilock brake system (ABS) maintains vehicle stability during operation which is incorporated herein by reference.
This wheel braking control apparatus is constituted as shown in FIG. 3. As illustrated, a master cylinder 50, which is driven in accordance with the operation of a brake pedal B, is connected to first and second wheel cylinders 52, 53 via a solenoid operated hydraulic valve 51 and hydraulic valves 63, 64, respectively, thus forming a brake fluid circuit 54. A circulating type anti brakelock circuit 56 including a pump 55 is connected to this circuit 54 to constitute the wheel braking control apparatus.
In the brake fluid circuit 54, the first and second cylinders 53, 53 respectively apply braking to right and left wheels 57, 58 of a vehicle. Rotation sensors S1 and S2 detect rotational speed of the wheels 57, 58 and so inform A controller C. During acceleration, the controller C controls the hydraulic valves 51 to prevent the wheels 57, 58 from spinning. If the wheels 57, 58 locked at the time braking is applied, the controller C controls the hydraulic valves 63, 64 to couple the cylinders 52, 53 to a reservoir to release the pressurized brake fluid.
In the brake fluid circuit, a fluid line 62 from the pump 55, a fluid line 59 connected to the first cylinder 52 and a line 60 connected to the second cylinder 53 join at junction 61. pressurized fluid from the pump 55 is evenly supplied to the first and second cylinders 52, 53 to control the rotation of the wheels 57, 58.
In operation of the ABS (after a locked wheel has been detected), there are occasions when an attempt is made to increase the fluid pressure on both wheel cylinders. At such times, there is a tendency for the pressurized fluid to favour one of the wheel cylinders, this temporarily causes a sharp drop of the fluid pressure in the other wheel cylinder. Such an imbalance causes improper brake control, thus making the braking of the wheels unstable.
In addition, when the hydraulic valve 51 is actuated, i.e., when the traction control (TRC) is executed, the pressures in the lines communicating with both wheel cylinders interferes with each other, thus presenting the same problem on braking of the wheels.